Use spring.factories to declare each test slice's auto-config imports

Closes gh-6001

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/ImportAutoConfiguration.java

@@ -26,7 +26,7 @@ import java.lang.annotation.Target;
 import org.springframework.context.annotation.Import;
 
 /**
- * Import and apply the selected auto-configuration classes. Applies the same ordering
+ * Import and apply the specified auto-configuration classes. Applies the same ordering
  * rules as {@code @EnableAutoConfiguration} but restricts the auto-configuration classes
  * to the specified set, rather than consulting {@code spring.factories}.
  * <p>
@@ -35,6 +35,7 @@ import org.springframework.context.annotation.Import;
  * and especially when writing tests.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  * @since 1.3.0
  */
 @Target(ElementType.TYPE)
@@ -46,9 +47,11 @@ import org.springframework.context.annotation.Import;
 public @interface ImportAutoConfiguration {
 
 	/**
-	 * The auto-configuration classes that should be imported.
+	 * The auto-configuration classes that should be imported. When empty, the classes are
+	 * specified using an entry in {@code META-INF/spring.factories} where the key is the
+	 * fully-qualified name of the annotated class.
 	 * @return the classes to import
 	 */
-	Class<?>[] value();
+	Class<?>[] value() default {};
 
 }

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/ImportAutoConfigurationImportSelector.java

@@ -27,6 +27,7 @@ import java.util.Set;
 
 import org.springframework.core.annotation.AnnotationAttributes;
 import org.springframework.core.annotation.AnnotationUtils;
+import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.util.ClassUtils;
 
@@ -77,19 +78,25 @@ class ImportAutoConfigurationImportSelector
 		if (source != null && seen.add(source)) {
 			for (Annotation annotation : source.getDeclaredAnnotations()) {
 				if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
-					collectCandidateConfigurations(annotation, candidates, seen);
+					collectCandidateConfigurations(source, annotation, candidates, seen);
 				}
 			}
 			collectCandidateConfigurations(source.getSuperclass(), candidates, seen);
 		}
 	}
 
-	private void collectCandidateConfigurations(Annotation annotation,
+	private void collectCandidateConfigurations(Class<?> source, Annotation annotation,
 			Set<String> candidates, Set<Class<?>> seen) {
 		if (ANNOTATION_NAMES.contains(annotation.annotationType().getName())) {
 			String[] value = (String[]) AnnotationUtils
 					.getAnnotationAttributes(annotation, true).get("value");
-			candidates.addAll(Arrays.asList(value));
+			if (value.length > 0) {
+				candidates.addAll(Arrays.asList(value));
+			}
+			else {
+				candidates.addAll(SpringFactoriesLoader.loadFactoryNames(source,
+						getClass().getClassLoader()));
+			}
 		}
 		collectCandidateConfigurations(annotation.annotationType(), candidates, seen);
 	}